Prevalence of proximal adenomas after an adenoma is found on flexible sigmoidoscopy

Adenomatous polyps are a precursor of colorectal cancer and a frequent finding on screening flexible sigmoidoscopy (FS). Performance of colonoscopy when a diminutive (<6mm) adenoma is found on FS has been the subject of considerable debate.

We retrospectively reviewed the data from our colorectal cancer screening program for patients with adenoma(s) found on FS. Patients were divided into three groups based on FS findings: (1) an adenoma <6mm in size, (2) multiple non-advanced adenomas or an adenoma 6-10mm in size, or (3) advanced adenoma defined as an adenoma >10mm or with villous histology or high-grade dysplasia or cancer. A comparison of the proximal findings was then made.

5291 FS reports were reviewed with 606 (12%) patients having at least one adenoma. Colonoscopy reports were available in 550 patients. Of the 258 patients with a diminutive distal adenoma, 69 (27%) had a proximal adenoma and 13 (5%) had an advanced proximal adenoma on colonoscopy. Of the 164 patients with an adenoma 6-10mm or multiple non-advanced adenomas, 59 (36%) had a proximal adenoma and 13 (8%) had an advanced proximal adenoma. Of the 128 patients with a distal advanced adenoma, 58 (45%) had a proximal adenoma and 15 (12%) had an advanced proximal adenoma. The increase in proximal adenomas across the three groups was significant (P=0.001), and there was a trend for increased prevalence of advanced adenomas (P=0.061).

The prevalence of proximal adenomas increased significantly with more advanced lesions found distally at FS, and there was a trend towards a higher prevalence of advanced proximal adenomas. Based on current guidelines, flexible sigmoidoscopy is a screening option that can be used to identify average-risk patients at increased risk of proximal neoplasia.